Image-forming devices capable of forming images by ejecting ink onto recording paper are well known in the art. The ink used in these image-forming devices is broadly divided among pigment inks and dye-based inks. However, pigment ink has a lower fixing property to paper than dye-based ink, which can lead to problems. For example, when printing on the back surface of the recording paper in duplex printing, pigment ink can become deposited on paper-conveying rollers that contact the printed top surface of the paper.
Pigment ink is often used for black ink (hereinafter referred to as “K ink”). Hence, due to the problem described above, it is important to adjust the density (usage quantity) of K ink to a value appropriate for the type of recording paper.
Specifically, the fixing property of ink can fluctuate due to differences in the type of recording paper, i.e., whether the paper is normal, special paper, or glossy, for example. Even among the same type of recording paper, the fixing property can vary, as in the case of normal paper produced by different manufacturers and according to different manufacturing methods. While it is possible to resolve the fixing problem for all types of recording paper by creating a color table with low quantity settings for K ink based on the recording paper with the lowest fixing property and using this color table for all types of recording paper, this method may lead to a separate problem of not being able to produce sufficient image quality (accurate color tones).
Another conceivable method involves creating a color table storing optimum black component values for each type of recording paper. However, since this method requires that tables be created and stored for all possible types of recording paper that can be used on the image-forming device, the number of steps for creating the color tables and the amount of memory usage would be enormous and, therefore, not practical.
In light of this problem, Japanese Patent Application Publication No. 2007-118238 discloses a technology for setting a lower color density (i.e., reducing the ink quantity) when performing duplex printing than when performing single-sided printing. As a result, ejected ink is absorbed by the recording paper, preventing ink on a printed surface of the recording paper from transferring onto paper-conveying rollers and the like when performing duplex printing.